The present invention pertains to a device for controlling the unrolling of the web in web-feeding devices provided with a web storage. Such a device can be preferably applied in a printing machine, particularly a rotary roller printing machine, in which the material web to be printed on is fed from a winding roller through a web storage of the printing machine with a constant and stable web tension.
Web-unrolling devices having a web storage with one group of rollers which are housing-fixed and are emptied or unloaded in the roller inoperative position and are then refilled, and another movable group of rollers have been known. A roller brake of the compensating roller in such devices is controlled and is arranged between the web storage and a web draw-in device, and the web unwinding takes place in dependence upon the web tension. Since speed fluctuations of the draw-in device or the unrolling roller affect the web tension, it has been proposed in EP-PS No. 169,476 that the effect of speed fluctuations would be prevented as early in operation as possible. In this device, depending on the change in the web tension the control system operates in response to measurements of the web in the draw-in device and the winding roller. However expenses resulting from the cascade-type control with receivers of reference and nominal values of the web tension and speed differences are considerable.
A substantial reduction of expenses is possible when the movable roller group of the web storage, in addition to its web-storing function can have the function of the reference value-transmitter for web speed changes. The disadvantage of such a device is that the deviation of the movable roller group of the web storage is proportional to the integral of the difference of the web speeds. The movable roller group of the web storage--of I-controller accordingly in the control system with the winding roller--or P-T.sub.1 --controller with a relatively great retardation tend to oscillate; these oscillations occur for a long time and do not decrease and can be changed within limits.